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Installing an AC Grounding System, Need Advice

Later this week, my electician will begin work on my electric project, which will involve the installation of a 7.5kVA isolation transformer that will be fed from a separate meter tap. The isolation transformer will be installed in front of a new dedicated circuit panel that will house the dedicated circuits that will feed my listening room. All the dedicated circuits will be fed from the same side of the bar in the new panel in order to maintain consistent phase.

As Sean has advised in a separate thread, I know it is important that I check - and upgrade as necessary - the ground for my AC system. (My house was built in the late 1950s, and, from the looks of things, not much has been done since that time to upgrade the electric service. So I am nearly certain that I will find the grounding system leaves much to be desired.) I also know from discussion in various other threads that it is important for the entire electrical system in my house to share a common ground. So I expect that I will need to upgrade the grounding system into my main circuit panel and then tie the isolation transformer and the new dedicated panel back to that same grounding system.

The work on my house is being performed by a qualified electrician, but, as I have noted in other threads, I would like advice on the audiophile details that can make a difference in the sound (in this case, the noise floor) of my system. Perhaps I should also mention that my plan involves installing a separate dedicated circuit for each of my seven components. Given that this sort of a set-up is more prone to ground loops, I am interested in advice regarding how to avoid them with this set-up.

With that as background, would any of the resident experts be willing to share with me the details of how to install a high quality grounding system for my AC power? I would appreciate as much detail as possible regarding the materials to use as well as installation advice.

I have read some advice in other threads recommending two separate copper grounding rods driven into the ground relatively close to each other with a weather-proofed connection between the two rods that is, in turn connected to the electrical system. I have also seen some advice that I believe involves wiring one of these connected ground rods to the main house circuit panel and the other connected ground rod to the audio portion of the system (i.e., in my case, the isolation transformer and the new dedicated circuit panel). Please let me know if this is headed in the right direction and, if so, please help me to fill in some details (dimensions of the copper, advice on how to drive it into the ground without mangling it, distance between the redundant rods, any other details you see fit).

As always, thanks for your help and patience.
cincy_bob

Showing 4 responses by cincy_bob

cincy_bob OP
270 posts
 
Jea48 and Shasta, thanks for your responses.

Jea48: The input to the isolation transformer will be 220V on the primary side. The transformer offers different taps to allow either 220V output or a stepped down 110V output on the secondary side. My electrician was planning to feed the new dedicated panel with the full 220V of output from the secondary side of the transformer. If this configuration does not make sense given my desire to run all the circuits from only one side of the bar, I would be interested in your observations and advice.

Regarding the water service in my house, it is metallic (copper) water service. I can see that there is a ground clamp on my water service ahead of the meter where the service enters my house. I believe that ground wire is tied into the ground for my AC service on the other side of the house. (I have not traced the wire in order to verify this; however, the ground wire runs in that general direction before it disappears above some non-removable ceiling tiles, so it is a safe bet.) I think I remember seeing a ground rod driven into the ground outside my house in the near vicinity of my electric service that I assume is also tied back to my main electric panel

Shasta: My house is not under construction. On the contrary, it was constructed in the late 1950s. As mentioned above, I believe my electric system is using a ground rod that is driven into the ground in the near vicinity of my electric service. Either I or my electrician will need to fish around in the ivy outside my house to verify the existence and location of that ground rod.
cincy_bob OP
270 posts
 
Shasta, I have done a little bit of research on the XIT grounding system that you suggested. It looks like a very serious product designed primarily for commercial and industrial use. Can you provide any further information on the practicalities - or "how to" - of using this product in a residential application? Do you have a ballpark estimate of what the 10-foot grounding system might cost, and what the incremental installation cost might be? Does this system require specialized installation skills beyond those of an ordinary electrician whose experience consists of more conventional grounding systems?

I would also be interested in a bit more education on your comment that "BTW, you'll never drive a rod yourself..." Is there specialized equipment involved in the installation of a ground rod? Does the process typically involve driving the rod into the ground (visions of driving a railroad spike)? Or, alternatively, does the proces involve boring a hole in the ground, placing the rod in the hole, and backfilling the hole? (Based on my limited reading on the XIT system, it seems that it is installed in the latter manner.)

Any further information you can offer would be much appreciated.
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cincy_bob OP
270 posts
 
Jea48, thanks for all your input. It is really valuable to me as I lack personal expertise in this area. Here are some answers to your questions:

1. Soil and Moisture - As my user name implies, I live in the Cincinnati, Ohio area. Our soil in this area involves a lot of clay. We tend to have normal midwestern weather with a fair amount of precipitation yearound but occasional droughts in the summer months. Let me know if additional information would be helpful in this area.

2. Isolation Transformer - My isolation transfomer is an MGE Topaz isolation transformer that is described in the following web link:

MGE Topaz 100 Installation and User Manual

This web link will lauch a pdf file that contains the full user manual for my isolation transformer. The specifications for the unit are contained on page 11 of the document. My unit is model no. T-100H-7500. It is a hardwired 7.5kVA transformer (see pg. 12 for the specifications of the various model numbers).

The unit provides 140dB of common mode noise attenuation and 65dB of normal mode noise attenuation. I believe the transformer also provides the electrostatic shielding that you mentioned in your latest post.

By the way, my use of the word, "taps," simply shows my inexperience with the subject matter. I had no technical basis for the use of that term.

Based on the advice in your latest post, it sounds like I should use the transformer to step down the 240V primary voltage to 120V at the output stage.

It would be a lot of help to me if you would explain a bit more to me about the primary and secondary grounding electrodes in my system. If I understand your posts to date, you are suggesting that, to comply with code and safety standards, the grounding electrode on the primary stage of the isolation transformer must be tied back to the grounding system at my main electric panel in my house (i.e., the clamp that is attached to my water pipe service where the service enters my house).

When you refer to the secondary grounding electrode, are you referring to a second ground connection from the secondary side of the isolation transformer? Did I understand your first post in this thread to suggest that it is best to have a ground for this secondary side of the transformer that is independent of the water pipe ground that is used as the primary ground for my electric system? I have seen a lot of cautionary advice about the use of two separate grounds within an electric system. The cautionary advice seems to say that it is never acceptable to have two separate grounding systems for two parts of an electrical system. Can you clarify this part for me?
cincy_bob OP
270 posts
 
Shasta, about a month ago, I hired a registered electrical engineer to develop drawings for the modifications to my residential electrical system. What I have been doing in this forum is educating myself so that I can raise the right topics with - and ask the right questions of - my electrical engineer and my electrician.

The service drawings for my system do not contain any detailed specifications for the grounding of the new circuit panel. Without the aid of this forum, I would not have known that there was any alternative to simply grounding the new panel back to the incoming water line that currently serves as the grounding electride for my electric system. And, without any discussion of the topic with my electrician, I am sure he would have opted for this single ground without any discussion and without me being aware of any alternative for a secondary ground. The education Jea48 has provided me regarding the option of installing a secondary outside new earth ground electrode allows me to have an intelligent conversation with my electric professionals that I could not otherwise have even initiated.

Jea48, thanks very much for all the information you have shared. It is very helpful to me and will significantly enhance my ability to communicate with my electrical engineer and electrician.
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